Supraventricular tachycardia and preexcitation syndromes, collectively referred to as SVT in this proposal, affect many children and young adults without underlying heart disease. Correspondingly, SVT ablation is the most frequent procedure performed by pediatric electrophysiologists. Fluoroscopy is used to guide catheters during ablation, but constitutes a significant source of radiation exposure and concomitant cancer risk. Nonfluoroscopic imaging (NFI) techniques are used for more complex ablation procedures, but their use to reduce fluoroscopy in SVT ablation has only been described in small, single-center studies. We propose a multi-center, prospective, single-blind, randomized non-inferiority trial in subjects ages 6 <21 years with normal hearts who are undergoing SVT ablation. Patients will be assigned to ablation using NFI augmented with fluoroscopy ("NFI strategy") or standard fluoroscopy ("standard therapy"), with randomization stratified by operator (attending electrophysiologist) and clinical SVT mechanism. Our primary hypothesis is that the NFI strategy is not inferior to standard therapy with respect to ablation failure. Data will be collected prior to, during and at discharge from the procedure, and at two months post randomization. Secondary outcomes include SVT recurrence two months after randomization and at trial end, the occurrence of adverse events, procedure times and charges, fluoroscopy time and radiation dose. The sample size is 714 subjects, and the necessary accrual period is conservatively estimated to be 22 months. All primary analyses will be performed on an intention-to-treat basis. For the primary endpoint, the risk difference will be estimated as the difference in the acute ablation failure rate between the NFI strategy and standard therapy, and a one-sided upper 95% confidence bound will be generated using the exact binomial method. This proposed non-inferiority trial may establish the efficacy of an alternative imaging pathway for SVT ablation, while minimizing the risk of severe late adverse sequelae from ionizing radiation. The knowledge gained in this study could revolutionize standard practice of ablation in all children, and serve as a paradigm for similar studies in other interventional disciplines. RELEVANCE: Ablation of supraventricular tachycardia (SVT) exposes otherwise healthy children to radiation, increasing their risk of cancer. We will compare ablation using non-fluoroscopic imaging to standard fluoroscopy, to explore whether radiation exposure can be substantially reduced without changing efficacy or safety of SVT ablation. This study will serve as a model for technology translation in pediatric catheter-based intervention.